As is known per se, the starters comprise a means of protection against the overcurrents taking the form of one or more electrical fuses and/or one or more circuit breakers. FIG. 1 thus shows an exemplary starter motor 1 comprising a fuse 2 mounted in series between a power supply terminal 3 of the electric machine 1 and of the windings 4.1-4.4 of the stator of said motor.
The fuse is intended to melt to cut the electrical power supply to the motor when it is passed through by a maximum predetermined current. This makes it possible to avoid damaging the starter or its environment because of the heat produced by an overcurrent. Such an overcurrent notably occurs in the case where the rotor of the motor is blocked in rotation.
When the machine is operating off-load or at low load (that is to say that it is operating approximately between 0 and 25% of the rated load), the off-load rotation speed of the rotor also leads to an overheating of the electric machine likely to damage the starter over time. This overheating, due notably to the mechanical friction between the brushes 6.1-6.4 and the collector, occurs for example in an overspeed phase when the pinion of the starter driven by the heat engine rotates more rapidly than the shaft driven by the rotor of the starter. However, in this case, the current passing through the fuse may be too low to cause the fuse 2 to melt, even over a long time.
The document FR140573 filed on 23th January by Valeo, describes a compact thermal protection system 5 that makes it possible to cut the electrical power supply of the motor in the abovementioned two cases (in case of blocking and in case of operation at low load). More specifically, this system is configured in such a way that, in the case of overheating, an overmoulded part on the plate of the brush-holder is deformed, such that the brush cages of positive polarity subject to the action of springs enter into contact with the plate linked to the terminal of negative polarity. A short circuit is thus created, causing the fuse of the starter to open.